president bashar al assad accusing oppositionists of using them in aleppo. the opposition pointing its collective finger to the syrian government. as both sides continue to squabble, u.s. government is trying to get proof that chemical weapons were use d. barbara starr is following all these developments for us. there's an interesting article in the "new york times" that says some american officials worried a lot about whether the syrian government was accusing rebels of using the weapons to prepare cover for its own future use of them, barbara. >> well, good morning, zoraida. that certainly is one consideration that u.s. officials are looking at, as they begin to conduct their own intelligence investigation into whether or not chemical weapons were used. as more pictures emerge of hospitalized syrians, u.s. intelligence agencies are in a massive, around-the-clock effort to determine if these people were attacked by chemical weapon s. so far, u.s. officials say there is no corroboration. >> so far, we have no evidence to substantiate the reports that chemica